[CI] Update GHPRB service user

Shared user sometimes been abused by other teams causing GitHub token exhaustion
This causes delays in GHPRB plug in response

Move to media team dedicated service user

Issue: HPCINFRA-3444

Signed-off-by: Michael Braverman <[email protected]>

Author: MrBr-github

.ci/opensource_jjb.yaml

@@ -122,7 +122,7 @@
             failure-status: "[FAIL]"
             error-status:   "[FAIL]"
             status-add-test-results: true
-            auth-id: 'swx-jenkins5_gh_token'
+            auth-id: 'svc-nbu-swx-media_GHPRB_ID'
             org-list: ["Mellanox"]
             white-list: ["swx-jenkins","swx-jenkins2","swx-jenkins3","mellanox-github"]
             black-list-target-branches: